Add a base_url option to ClientSession (#6129)

Co-authored-by: Andrew Svetlov <[email protected]>
Co-authored-by: Sviatoslav Sydorenko <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

CHANGES/6013.feature

@@ -0,0 +1 @@
+Added ``base_url`` parameter to the initializer of :class:`~aiohttp.ClientSession`.

aiohttp/client.py

@@ -166,6 +166,7 @@ class ClientSession:
 
     ATTRS = frozenset(
         [
+            "_base_url",
             "_source_traceback",
             "_connector",
             "requote_redirect_url",
@@ -194,6 +195,7 @@ class ClientSession:
 
     def __init__(
         self,
+        base_url: Optional[StrOrURL] = None,
         *,
         connector: Optional[BaseConnector] = None,
         loop: Optional[asyncio.AbstractEventLoop] = None,
@@ -218,13 +220,20 @@ def __init__(
         trace_configs: Optional[List[TraceConfig]] = None,
         read_bufsize: int = 2 ** 16,
     ) -> None:
-
         if loop is None:
             if connector is not None:
                 loop = connector._loop
 
         loop = get_running_loop(loop)
 
+        if base_url is None or isinstance(base_url, URL):
+            self._base_url: Optional[URL] = base_url
+        else:
+            self._base_url = URL(base_url)
+            assert (
+                self._base_url.origin() == self._base_url
+            ), "Only absolute URLs without path part are supported"
+
         if connector is None:
             connector = TCPConnector(loop=loop)
 
@@ -343,6 +352,14 @@ def request(
         """Perform HTTP request."""
         return _RequestContextManager(self._request(method, url, **kwargs))
 
+    def _build_url(self, str_or_url: StrOrURL) -> URL:
+        url = URL(str_or_url)
+        if self._base_url is None:
+            return url
+        else:
+            assert not url.is_absolute() and url.path.startswith("/")
+            return self._base_url.join(url)
+
     async def _request(
         self,
         method: str,
@@ -402,7 +419,7 @@ async def _request(
         proxy_headers = self._prepare_headers(proxy_headers)
 
         try:
-            url = URL(str_or_url)
+            url = self._build_url(str_or_url)
         except ValueError as e:
             raise InvalidURL(str_or_url) from e
 

docs/client_quickstart.rst

@@ -55,6 +55,18 @@ Other HTTP methods are available as well::
     session.options('http://httpbin.org/get')
     session.patch('http://httpbin.org/patch', data=b'data')
 
+To make several requests to the same site more simple, the parameter ``base_url``
+of :class:`ClientSession` constructor can be used. For example to request different
+endpoints of ``http://httpbin.org`` can be used the following code::
+
+    async with aiohttp.ClientSession('http://httpbin.org') as session:
+        async with session.get('/get'):
+            pass
+        async with session.post('/post', data=b'data'):
+            pass
+        async with session.put('/put', data=b'data'):
+            pass
+
 .. note::
 
    Don't create a session per request. Most likely you need a session

docs/client_reference.rst

@@ -38,7 +38,8 @@ Usage example::
 
 The client session supports the context manager protocol for self closing.
 
-.. class:: ClientSession(*, connector=None, loop=None, cookies=None, \
+.. class:: ClientSession(base_url=None, *, \
+                         connector=None, cookies=None, \
                          headers=None, skip_auto_headers=None, \
                          auth=None, json_serialize=json.dumps, \
                          version=aiohttp.HttpVersion11, \
@@ -56,6 +57,11 @@ The client session supports the context manager protocol for self closing.
    The class for creating client sessions and making requests.
 
 
+   :param base_url: Base part of the URL (optional)
+      If set it allows to skip the base part in request calls.
+
+      .. versionadded:: 3.8
+
    :param aiohttp.BaseConnector connector: BaseConnector
       sub-class instance to support connection pooling.
 

tests/test_client_session.py

@@ -862,3 +862,39 @@ async def test_requote_redirect_setter() -> None:
         session.requote_redirect_url = False
     assert not session.requote_redirect_url
     await session.close()
+
+
+@pytest.mark.parametrize(
+    ("base_url", "url", "expected_url"),
+    [
+        pytest.param(
+            None,
+            "http://example.com/test",
+            URL("http://example.com/test"),
+            id="base_url=None url='http://example.com/test'",
+        ),
+        pytest.param(
+            None,
+            URL("http://example.com/test"),
+            URL("http://example.com/test"),
+            id="base_url=None url=URL('http://example.com/test')",
+        ),
+        pytest.param(
+            "http://example.com",
+            "/test",
+            URL("http://example.com/test"),
+            id="base_url='http://example.com' url='/test'",
+        ),
+        pytest.param(
+            URL("http://example.com"),
+            "/test",
+            URL("http://example.com/test"),
+            id="base_url=URL('http://example.com') url='/test'",
+        ),
+    ],
+)
+async def test_build_url_returns_expected_url(
+    create_session, base_url, url, expected_url
+) -> None:
+    session = await create_session(base_url)
+    assert session._build_url(url) == expected_url